A conventional communications network, for example a broadband communications network comprises a plurality of physical resources in the form of network elements, eg switches, cross connects, regenerators, repeaters, transmission links such as fiber optic links or coaxial cable links, operating under control of a plurality logical resources, eg transport protocols, and local controls associated with individual physical resources. An example of a generic representation of a communications network is illustrated schematically in FIG. 1 herein, in which the physical resources of a core network are located at a plurality of nodes 100 and links 101 distributed over a geographical area. For a network operator to maintain control of a communications network for its operation, administration and maintenance, a management system is maintained which stores information describing the physical and logical resources within the network. One or more management systems may reside at a centralized location, eg a network controller 102, or different management systems may be situated at a plurality of network controllers at different locations. The management system stores data describing each individual network element in a communications network and has one or more management applications which use the data to manage various aspects of the network, eg operation, administration, and maintenance of the network. A conventional communications network may comprise of the order of hundreds of individual network elements, eg switches, cross connects, regenerators, each of which contains of the order of tens to hundreds of cards, having processors, line terminations, buffers, registers, switch fabrics, etc. each card containing of the order of hundreds of individual components. In general, a conventional communications network may comprise a multitude of different legacy equipment types of different proprietary manufacture, each of which has its own particular internal configuration and offers its own specific capabilities.
International Telecommunications Union (ITU-T) recommendation G.805 of November 1995, (available from International Telecommunication Union, General Secretariat, Sales Service, Place de Nation, CH 1211, Geneva 20, Switzerland), sets out a functional architecture for telecommunications transport networks in a technology independent manner. A generic functional architecture is set out as a basis for a harmonized set of functional architecture recommendations for broadband transport network including asynchronous transfer mode (ATM), synchronous digital hierarchy (SDH) and plesiochronous digital hierarchy (PDH), as well as a corresponding set of recommendations for management, performance analysis and equipment specification for such transport networks. In general, in known transport networks circuit switched communications are made on an end to end basis over a plurality of network entities. In this specification, by circuit switched, it is meant that the network reserves part of its resources for the purpose of supporting an end to end communication, for the duration of that communication, whether those resources are used or not.
Referring to FIG. 2 herein, there is illustrated a simple example of a trail of a circuit switched communication over part of a communications transport network. A transport network is defined in recommendation G.805 as "the functional resources of the network which conveys user information between locations". In recommendation G.805, a trail is defined as "a transport entity which consists of an associated pair of unidirectional trails capably of simultaneously transferring information in opposite directions between their respective inputs and outputs". A unidirectional trail is defined as a "transport entity" responsible for the transfer of information from the input of a trail termination source to the output of a trail termination sink. The integrity of the information transfer is monitored. It is formed by combining trail termination functions and a network connection. A transport entity is defined as "an architectural component which transfers information between its inputs and outputs within a layer network. A layer network is defined as "a topological component that includes both transport entities and transport processing functions that describe the generation, transport and termination of a particular characteristic information. A connection is defined as "a transport entity which consists of an associated pair of uni-directional connections capable of simultaneously transferring information in opposite directions between their respective inputs and outputs. A uni-directional connection is defined as "a transport entity which transfers information transparently from input to output".
In FIG. 2 herein, there is illustrated schematically a plurality of transport entities 200, 201, 202, 203, 204 in a communications network comprising network elements eg switches, cross connects, links, supporting an end to end trail between first and second trail termination points 205, 206. The trail is carried over a plurality of connections, which connect the transport entities to each other. Connections between transport entities terminate at a plurality of connection termination points (CTP) within the transport entities. The generalized trail as illustrated in FIG. 2 herein, incorporates different trails in different transport protocols. For example, virtual paths and virtual circuits in asynchronous transfer mode constitute trails within the meaning of ITU-T Recommendation G.805. ATM cells may be carried within a virtual path within SDH frames over an SDH trail.
Within a layered network protocol trails occur within layers. Trails can occur at a plurality of different layers, however each trail is always contained within its own layer. In a large network, comprising tens to hundreds of network elements, management of end to end trails poses a highly complex problem and poses difficulties in the practical implementation of setting up and tearing down of trails. The concept of trail management is mentioned in recommendation G.805 in which a trail management process is defined as "configuration of network resources during network operation for the purposes of allocation, reallocation and routing of trails to provide transport to client networks." Conventionally, for creation of a trail across a network it is known for several network operators, at several network controllers controlling different sections of the network, to each set up one or more connections within sections of the network which they control. To achieve a trail over a large number of transport entities, a network operator wishing to set up a trail may need to contact, by means of a telephone call or a fax, other network operators having control of other parts of the network across which a trail may pass, and coordinate the setting up of a trail by verbal or fax communication with the other human network operators.
In conventional prior art network management systems, it is known to keep a master database which always overwrites whatever connections exist in the real network under management. Thus, if a network operator makes changes to connections or trails in a network by configuring an individual network element directly, the conventional network management system database will attempt to overwrite any changes made at the network element level, regardless of whether the network operator intended those changes to the network element or not. Further, the known network management systems do not provide an ability to draw configuration and connectivity information from the real network, and do not compare such information with the information kept in the master database.
Prior art network management systems either represent network configurations which a network operator plans at a network controller, and implements those configurations irrespective of existing configurations of a network, or provide a network operator with data describing actual network configurations, without taking into account or making provision for a network operator's planned or intended present and future configurations of the network.